I have been a mod at a few other large forums and the thing that I found killed alot of the spam bots is using the 5 post count confirmation ability.
Its a setting in the Admin section that states that every member must confirm they are not a bot for 5 posts then it goes away. Spam bots usually just sign up, confirm, then try to make a single post. The secondary confirmation kills its ability to do make the post.
If you want you can set up as an admin and I can help out, then afterwards you can remove my mod rights.
Not to mention I am also a CDT Agent for Shadowrun, and I also help set up my Firebase's forum.